It is known that absorber particles e.g. hydrophilic acrylamide polymers, are added to soil for the purpose of water retention in sandy soils, in order to reduce the quantity or water which sinks to a level beyond the reach of roots.
Similarly for retention, suitable gel granulates are added to various substrates used for grass covering of roofs to ensure sufficient water supply for the plants despite a relatively small volume of substrate (e.g. EP 369062).
However, freely mixing absorbers into vegetation substrates does not allow fixing of the absorber particles at a defined level in the substrate layer. Because the absorber particles wander, they become irregularly distributed in the substrate which has a negative effect on the retention capacity. Simultaneously, the volume alteration resulting from the absorption of water results in repeated shifting of the substrate particles within the vegetation structure and thus causes damage to the capillary root system. The shifting of the absorber particles can also impair the local stability of the vegetation substrate.